The ioslides presentation in Rmarkdown enables the use of interactive assets and greatly boosts reproducibility of slides across presentations. A tutorial on ioslides presentation can be found in the R Markdown: The Definitive Guide.
The following single character keyboard shortcuts enable alternate display modes:
f: enable fullscreen mode (in the web browser press ctrl + + to zoom-in or ctrl + - to zoom-out)
w: toggle widescreen mode (format can be set to 16:9 or 16:10 in the output, as shown above for 16:9)
o: enable overview mode
h: enable code highlight mode
p: show presenter notes
Pressing Esc exits all of these modes. See the sections below on Code Highlighting and Presenter Mode for additional detail on those modes.